Conventional methods of adequate power factor correction (PFC), especially for consolidated (single-stage) AC/DC converters, include contributions described in U.S. patents and/or in technical reports.
Notable patented examples include the following: "Single Conversion Power Factor Correction Using SEPIC Converter" by Fraidlin, Slack and Wadlington in U.S. Pat. No. 5,115,185 (1992)--good power factor but low-frequency ripple in output voltage and slow transient response; also "High Power Factor AC/DC Converter" by Teramoto, Sekine, and Saito in U.S. Pat. No. 5,301,095 (1994)--a PFC corrective design with a sole high-frequency capacitor, but the primary diode undergoes hard switching unsuited to high-frequency operation, while input and load ranges are narrow in the absence of extensive frequency modulation; and, more recently, "Input Harmonic Current Corrected AC-to-DC Converter with Multiple-Coupled Primary Windings" by Ho and Lee in U.S. Pat. No. 5,600,546 (1997)--a single-stage PFC AC/DC converter with one power switch and one magnetic component, its energy-storage capacitor so highly voltage-stressed as to limit power factor to about 0.8, and pulsating input with high switching AC ripple requiring optimal EMI filtration, and with the switching diode undergoing hard switching.
Notable examples of contributions to the technical literature include "Integrated High Quality Rectifier-Regulators" by Madigan, Erickson, and Ismail in their 1992 PESC Record article describing so-called BIFRED (and BIBRED)--designs of very good power factor and regulation, but not so good efficiency, and also nearly as bulky as earlier designs; also "A New Family of Single-Stage Power-Factor Correctors with Fast Regulation of the Output Voltage" by Redl, Balogh, and Sokal in their 1994 PESC Record article--teaching PFC correction with a sole diode, but imposing high switching stresses because of deep discontinuous conduction and requiring a large EMI filter, very bulky; and also, more recently, "Single-Stage Single-Switch Isolated Power Supply Technique with Input-Current Shaping and Fast Output-Voltage Regulation for Universal Input-Voltage-Range Operations" by Huber and Jovanovic in their 1997 APEC Proceedings IEEE article--describing a converter reasonably capable of 0.9 power factor and 400 V capacitors but requiring a complicated power transformer, with at least three primary windings, heavily dependent upon transformer leakage inductance, very resistant to adequate control.
My present invention relies heavily upon reduction in number of components via intermediate tapping of transformer primary windings.